drm/msm/dpu: Change _dpu_crtc_vblank_enable_no_lock to void

Removes redundant tests for _dpu_crtc_vblank_enable_no_lock.
Function return type is now void and all function calls have
been changed accordingly.

Signed-off-by: Bruce Wang <bzwang@chromium.org>
Reviewed-by: Sean Paul <seanpaul@chromium.org>
Signed-off-by: Sean Paul <seanpaul@chromium.org>
Signed-off-by: Rob Clark <robdclark@gmail.com>